Dynamic Programming solution to problem http://codeforces.com/problemset/problem/22/B

c.cpp

#include <bits/stdc++.h>

using namespace std;

char b[28][28];
int dp[28][28], n, m, r;

int main() {
  cin >> n >> m;
  for (int i = 1; i <= n; ++i) {
    for (int j = 1; j <= m; ++j) {
      cin >> b[i][j];
      b[i][j] = b[i][j]-'0' ? 0 : 1;
      if (b[i][j]) dp[i][j] = dp[i][j-1]+1;
    }
  }
  for (int i = n; i >= 1; --i) {
    for (int j = m; j >= 1; --j) {
      int w = 28, p = 0;
      for (int h = 1; b[i-h+1][j]; ++h) {
        w = min(w, dp[i-h+1][j]);
        p = max(p, h+w);
      }
      r = max(r, p);
    }
  }
  cout << 2*r << endl;
  return 0;
}